Dykema said Saturday’s maddening weather pattern, with summer fog advancing and retreating throughout the day before advancing for good when the sun goes down, will hold true for Sunday and Monday and maybe throughout the week.

“The western half of San Francisco should stay cloudy all day,” he said. “Everything east of Twin Peaks will clear out in the early afternoon and stay clear until early evening.”

The culprit is a weak low-pressure trough stuck along the coastline from Marin to Monterey. That has caused the marine layer to build to 2,000 feet, maybe twice as thick as normal for this time of year. On the plus side, Dykema said there is hope that the fog will be higher off the water than last year, leaving around 500 feet of clearance.

“You might be able to see the lower fireworks,” he said, “but the higher ones will be in the clouds.”